Various reinforcement fibers and their use in a wide variety of applications are known in the art. For example, it is known to add reinforcement fibers to materials, such as concrete, including asphalt cement concrete and Portland cement concrete and the like, to add strength, toughness, and durability, and to improve the integrity of the cement properties. Typical reinforcement fibers that are added to concrete include, for example, asbestos fibers, glass fibers, steel fibers, mineral fibers, natural fibers, synthetic fibers (such as polymer and aramid fibers), and cellulose fibers. Some reinforcement fibers are better suited for particular applications than others. For example, asbestos fibers are known to provide effective reinforcement but, due to environmental and health concerns, these fibers are not extensively used. In addition, some fibers are relatively expensive and as a result, their commercial use is limited.
Reinforcement fibers are also generally known for use in the drilling industry. Oil, gas and other subterranean wells are made by drilling a borehole into the ground. A rotating drill is typically used to form the borehole. As the rotating drill works its way through geological formations, debris from the cuttings, such as, rock, dirt and clay, accumulates and fills the hole. A liquid, such as, fresh water, salt water or a water and oil mixture, is circulated downwardly through a drill pipe and drill bit and then upwardly through an annulus created between the drill pipe and the wall of the borehole. Circulation of the liquid is effective to carry debris out of the borehole, and simultaneously to cool and lubricate the drill. However, the liquid alone is typically not effective to remove a sufficient amount of debris and other mechanisms are employed to enhance debris removal. For example, to improve the level of debris removal, additives are injected within the liquid through the drill pipe into the well bore. It is known in the art to use reinforcement fibers as an additive to drilling liquids to increase the levels of debris removal. The addition of reinforcement fibers to drilling liquids increases the carrying capacity without increasing the viscosity of the liquid.
In addition to their role as an additive for debris removal, reinforcement fibers also may be added to drilling liquids/fluids as a lost circulation material. Lost circulation generally refers to the undesirable loss of at least a portion of drilling fluid into the subterranean formation penetrated by the well bore. Thus, the addition of reinforcement fibers is effective to prevent fluid loss through fissures and pores in the geological formations.
In addition to, or instead of, adding reinforcement fibers to the drilling liquid/fluid, the fibers can be incorporated as a lost circulation material into the cement which is used in drilling wells. In drilling a well, a pipe string (e.g., casing and/or liner) may be run into a well bore and cemented in place. A cement composition is pumped into an annulus between the walls of the wellbore and the exterior surface of the pipe string disposed therein. The cement composition sets in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement that supports and positions the pipe string in the wellbore and bonds the pipe string surface to the subterranean formation. The annular sheath of set cement surrounding the pipe string functions to prevent the migration of fluids in the annulus. The presence of reinforcement fibers in the cement can reduce or preclude voids or cracks in the cement and therefore, reduce or preclude the flow of liquids there through.
It has been found in accordance with the present invention that reinforcement fibers provide benefits to known cementitious compositions. Typically, such compositions consist of water, cement, sand and optionally color or pigment, which can be mixed wet into thick emulsions which harden over time. There are a wide variety of cementitious compositions and uses for these materials. For example, cementitious compositions include, but are not limited to, grout compositions. There are varied uses for grout known in the art, such as, to embed rebars in masonry walls, connect sections of precast concrete, and fill voids and seal joints, such as between tiles. Structural grout is often used in reinforced masonry to fill voids in masonry housing reinforcing steel, securing the steel in place and bonding it to the masonry. Non-shrink grout is used beneath metal bearing plates to ensure a consistent bearing surface between the plate and its substrate.
In certain embodiments, grout compositions are used to anchor bolts for various structures into a variety of substrates. For example, grout is used to anchor power line tower support bolts and guy wires to the earth. In certain other embodiments, grout compositions are used in micro-piles in the earth that consist of holes in the range of from 15 to 80 feet in depth. The hardened piles then serve as support connections for electrical transmission line structures. In these embodiments, the grout composition is often in the form of a liquid. The liquid grout is used to fill hollow cavities or holes. With known grout compositions, leakage through porous and fractured rock within the earthen substrate has occurred. As a result, a significant portion of the grout used to fill the cavities can be lost. Since considerably more grout needs to be used than estimated, the cost associated with the grout leakage and losses can be significant. Thus, there is a need in the art to improve grout compositions such that they remain flowable during insertion and placement, and then thicken in order to reduce or preclude losses due to leakage into undesired zones. In general, it is desirable to form a grout composition that is thixotropic in nature such that the grout flows readily when in a liquid form, is transformed to a gel when static and subsequently returns to a liquid when forced to move. Further, it is advantageous for the grout composition to plug-off cavities to prevent leakage there through.
It is known in the art to use polyolefin fibers as lost circulation material because they are readily available. However, polyolefin fibers tend to be difficult to dry blend with cement. Further, it has been found that polyolefin fibers agglomerate in dry cement when it is conveyed causing plugging to occur, and when the cement and fibers are combined with mixing water, the fibers can have a tendency to clump which can prevent their dispersion into and throughout the cement composition. The lack of dispersion of the fibers in the cement composition can make it difficult to pump. In an attempt to improve dry blending, various compositions and methods have been developed for surface treating the hydrophobic fibers to render them hydrophilic.
There is a need to develop improved or enhanced fibers as lost circulation material that can easily disperse in cementitious or grout compositions and drilling fluids, and are suitable for dry blending in commercial applications, whether treated or untreated.